The present invention relates to a method of burning solid, liquid, or gaseous fuels, especially coal dust or pulverized coal, and includes the steps of tangentially introducing main fuel via main burners into a combustion chamber, where the fuel is burned, introducing reducing fuel via reduction burners into the combustion chamber to reduce the nitrogen oxides produced during the combustion of the main fuel, with the reducing fuel being burned under partial stoichiometric conditions, and, to ensure the burning-out of the fuel introduced into the combustion chamber, introducing burn-out air above the feed of the main fuel and the reducing fuel, with a helically rising flow being provided in the combustion chamber. The present invention also relates to tangential firing equipment, especially for carrying out the aforementioned method; this equipment has a plurality of main burners oriented in conformity with a burning circle, a plurality of reduction burners, and a plurality of burn-out air nozzles disposed above the reduction burners.
A method of the aforementioned general type is known from the publication "Development of Mitsubishi" "Mact n-furnace NO.sub.x -removal process for steam and generators" from "Proceedings of the 1982 joint symposium on stationary Combustion NO.sub.x control".
With the heretofore known way of carrying out such a method, there is formed in the combustion chamber, from the bottom toward the top, a main burner combustion zone, a nitrogen oxide reduction zone in which the reducing fuel is burned under partial stoichiometric conditions, and a burn-out zone above the feed for the burn-out air. With the heretofore known firing equipment for carrying out such a method, there are disposed in a given burner plane, i.e. in a vertical plane, one above the other a main burner, a reduction burner, and a burn-out air nozzle (see in particular FIG. 20 of the cited reference). It has been proven that the large-scale application of such a fuel stage encounters difficulties. For example, the gaseous and solid materials in the combustion chamber move upwardly along a helical path, so that when the reduction burner is disposed in the same vertical plane as the main burner or burners, there is no assurance that the reducing fuel can reduce the NO.sub.x that is formed further below, since the reducing fuel no longer comes into contact with this NO.sub.x. Thus, with the heretofore known method the introduction of the reducing fuel is largely effected without taking into consideration the position of the primary flames in the lower portion of the combustion chamber in which the NO.sub.x is formed. This localized independence primarily involves drawbacks when, during partial-load operation, some of the burners are turned off, because then it is no longer possible to achieve a good intermixing between the fuel gases of the primary combustion zone and the reducing fuel.
Furthermore, the fact that the reduction burners are disposed above the main burners in the same burner plane requires a relatively high combustion chamber.
It is an object of the present invention to provide a method where on the one hand it is possible to achieve sufficient reduction of the nitrogen oxide level, and on the other hand even at partial load there is assured a good intermixing of the reducing fuel in the primary flames of the main burners.